src/gromacs/random/seed.h

   1 /*
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   5  * Mark Abraham, David van der Spoel, Berk Hess, and Erik Lindahl,
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  35
  36 /*! \file
  37  * \brief Random seed and domain utilities
  38  *
  39  * This file contains utilities to create true random seeds from the system,
  40  * and logic to keep track of different random domains for random engines such
  41  * as ThreeFry that can take a second seed value.
  42  *
  43  * \author Erik Lindahl <erik.lindahl@gmail.com>
  44  * \inpublicapi
  45  * \ingroup module_random
  46  */
  47
  48 #ifndef GMX_RANDOM_SEED_H
  49 #define GMX_RANDOM_SEED_H
  50
  51 #include <random>
  52
  53 #include "gromacs/utility/basedefinitions.h"
  54
  55 namespace gmx
  56 {
  57
  58 /*! \brief Return 64 random bits from the random device, suitable as seed.
  59  *
  60  *  If the internal random device output is smaller than 64 bits, this routine
  61  *  will use multiple calls internally until we have 64 bits of random data.
  62  *
  63  *  \return 64-bit unsigned integer with random bits.
  64  */
  65 uint64_t
  66 makeRandomSeed();
  67
  68 /*! \brief Random device
  69  *
  70  *  For now this is identical to the standard library, but since we use
  71  *  the GROMACS random module for all other random engines and distributions
  72  *  it is convenient to have this too in the same module.
  73  */
  74 typedef std::random_device RandomDevice;
  75
  76 /*! \brief Enumerated values for fixed part of random seed (domain)
  77  *
  78  *  Random numbers are used in many places in GROMACS, and to avoid identical
  79  *  streams the random seeds should be different. Instead of keeping track of
  80  *  several different user-provided seeds, it is better to use the fact that
  81  *  generators like ThreeFry take two 64-bit keys, and combine a general
  82  *  user-provided 64-bit random seed with a second constant value from this list
  83  *  to make each stream guaranteed unique.
  84  *
  85  *  \note There is no reason to go overboard with adding options; we only
  86  *        need to guarantee different streams for cases that might be present
  87  *        simultaneously in a single simulation. As an example, two different
  88  *        integrators (or thermostats) can reuse the same domain.
  89  *  \note When you do add options, leave some space between the values so
  90  *        you can group new options with old ones without changing old values.
  91  */
  92 enum class RandomDomain
  93 {
  94     Other                    = 0x00000000,   //!< Generic - stream uniqueness is not important
  95     MaxwellVelocities        = 0x00001000,   //!< Veolcity assignment from Maxwell distribution
  96     TestParticleInsertion    = 0x00002000,   //!< Test particle insertion
  97     UpdateCoordinates        = 0x00003000,   //!< Particle integrators
  98     UpdateConstraints        = 0x00004000,   //!< Second integrator step for constraints
  99     Thermostat               = 0x00005000,   //!< Stochastic temperature coupling
 100     Barostat                 = 0x00006000,   //!< Stochastic pressure coupling
 101     ReplicaExchange          = 0x00007000,   //!< Replica exchange metropolis moves
 102     ExpandedEnsemble         = 0x00008000,   //!< Expanded ensemble lambda moves
 103     AwhBiasing               = 0x00009000    //!< AWH biasing reference value moves
 104 };
 105
 106 }      // namespace gmx
 107
 108 #endif // GMX_RANDOM_SEED_H